Touch sensing is a key technology in the implementation of sophisticated modern human-machine interfaces. Touch sensing can involve sensing the proximity, contact, and/or position of an object such as, for example, a human digit (i.e., a finger or thumb), stylus or other input object. Multitouch sensing can involve similar sensing with respect to multiple simultaneous input objects.
In many modern systems, touch sensing is substantially limited to sensing of human digits, as smaller objects such as a stylus cannot be adequately differentiated for treatment in a different manner. In many touch screen applications, relatively large fingers can occlude the comparatively small user interface elements that the human digits(s) are trying to interact with. Using a stylus or similar input object in such a situation would seem to resolve such a problem, as stylus input can provide higher-precision user input. However, lack of adequate or any stylus input mode is a deficiency in many common two-dimensional capacitive touch sensors. Many current stylus input solutions simply attempt to address this issue by: 1) requiring use of a an active stylus; or 2) requiring use of a stylus with a relatively fat tip to mimic a capacitive response caused by a human digit; or 3) adding additional sensor elements to the capacitive touch sensor. The first case typically involves tethered styli which adds expense, limits user input flexibility, and increases complexity of a device. The second case only substitutes a different input device which may suffer from the same problems as a human digit. The third case increases complexity/cost of the sensing region of the sensor by requiring a specialized sensor pattern to deal with a narrow stylus tip.